Since clean and inexhaustible solar energy can be directly converted into electrical energy, solar cells are expected to become a new energy source.
Heretofore, there has been known a solar cell including intrinsic semiconductor layers (i-type semiconductor layers) formed on both principal planes of a substrate made of a crystalline semiconductor and made of an amorphous semiconductor without addition of a dopant. In this solar cell, a first-conductivity type semiconductor layer (such as an n-type semiconductor layer) is formed on top of the i-type semiconductor layer formed on one principle plane. A second-conductivity type semiconductor layer (such as a p-type semiconductor layer) is formed on top of the i-type semiconductor layer formed on the other principal plane.
Plasma chemical vapor deposition (hereinafter referred to as plasma CVD) is generally used as a method for manufacturing such a solar cell (Patent Document 1, for example).
Specifically, a substrate made of single crystalline silicon is conveyed into a first reaction chamber. At this time, in order to form the semiconductor layer only on the one principle plane of the substrate, the other principle plane of the substrate is covered with a tray, for example. The i-type semiconductor layer is formed on the first principal plane of the conveyed substrate by plasma CVD. The substrate on which the i-type semiconductor layer is formed is conveyed into a second reaction chamber. After conveyance, the first-conductivity type semiconductor layer is formed on top of the i-type semiconductor layer by plasma CVD. The substrate on which the first-conductivity type semiconductor layer is formed is taken out of the second reaction chamber. Subsequently, in order to form the semiconductor layer only on the other principle plane of the taken-out substrate, the one principle plane of the substrate is covered with a tray, for example. The substrate having its first principal plane covered is conveyed into the first reaction chamber. The i-type semiconductor layer is formed on the other principal plane of the conveyed substrate by plasma CVD. The substrate having the i-type semiconductor layer formed on the other principle plane thereof is conveyed into a third reaction chamber. After conveyance, the second-conductivity type semiconductor layer is formed on top of the i-type semiconductor layer by plasma CVD. The substrate having the first-conductivity type semiconductor layer and the second-conductivity type semiconductor layer formed thereon is taken out of the third reaction chamber. A transparent conductive film having optical transparency, such as an ITO, is formed by sputtering on top of each of the first-conductivity type semiconductor layer and the second-conductivity type semiconductor layer. A collecting electrode is formed by screen printing on each of the transparent conductive films. A solar cell has been manufactured through these processes.
Note that the semiconductor layer of the first conductivity type is of any conductivity type of p-type and n-type, and the second conductivity type is the other conductivity type.